chapter twenty four

24 Working with Option: for-comprehension

 

After reading this lesson, you will be able to:

  • Chain optional values together using for-comprehension.
  • Introduce conditions within for-comprehension constructs
  • Code using the most common operations defined on Option

In the previous lesson, you have learned how to use the functions map, flatten, and flatMap to manipulate optional values. In this lesson, you are also going to discover a more readable and elegant way of combining instances of Option thanks to a new type of construct, called “for-comprehension”. You’ll also see how to integrate Boolean conditions to control further how the values are chained together. Finally, you’ll discover other useful operations implemented for Option, such as isDefined, getOrElse, find, and exists. In the capstone, you will use the function getOrElse on Option to provide an alternative message for your HTTP request when a draw of the game “Paper, Rock, Scissors, Lizard, Spock!” occurs.

Consider this

Assume you have implemented a function to combine many (e.g., five or more) optional values in an ordered sequence using flatMap. Can you think of any aspect of your implementation that could make your code difficult to maintain and read?

24.1  For-comprehension on Option

In the previous lesson, you have discovered the flatMap function and how you can use it to concatenate optional operation together. Let’s have a look at the code in listing 23.8:

24.1.1    For-comprehension as syntactic sugar for nested map and flatMap calls

24.1.2    Filtering values within For-Comprehension

24.2  Other operations on Option

24.3  Summary

24.4  Answers to Quick Checks